Systems and methods for treating waste water

ABSTRACT

Systems and methods for treating waste water containing biological wastes such as animal waste generated in livestock-raising operations, wherein the waste water is subjected to a series of operations to separate solids from the liquid phase of the waste water and to biologically treat the waste water to break down organic components. The separated solids are stored for further treatment or conversion into useful materials. The treated liquid phase can be put to various uses. In one embodiment, the treated liquid is recycled as flush water for flushing animal waste from an animal barn, whereby little or no liquid phase escapes the system into the surrounding environment.

FIELD OF THE INVENTION

The invention relates to the treatment of waste water, which may includebiological waste, and more particularly may include animal wastegenerated in the raising of livestock.

BACKGROUND OF THE INVENTION

In large-scale animal husbandry operations, substantial amounts ofanimal waste are generated. Modem methods of raising livestockfacilitate capturing that waste in such a way that treatment of thewaste can be undertaken. For example, hogs often are now raised in“high-density” hog barns each of which can hold several hundred animals.Such hog barns are usually equipped with slotted floors that allowanimal waste to pass through the floor into a space below. A flushsystem is operated periodically to flush the waste from the subfloorspace using water. Once flushed from the hog barn, the waste can behandled in various ways depending on the particular installation.

Often the waste is simply pumped into a large lagoon near the barn,where it undergoes a slow anaerobic digestion. The treated waste thenmay be sprayed onto fields. A drawback of such lagoons is that duringcertain weather conditions, such as hurricanes or flooding, the wastewater can be displaced from the lagoon into the surrounding environment.

It would be beneficial if the total amount of waste entering theenvironment surrounding a livestock-raising operation could be reduced.

SUMMARY OF THE INVENTION

The invention addresses the above needs and achieves other advantages,by providing systems and methods for treating waste water containingbiological wastes such as animal waste generated in livestock-raisingoperations, wherein the waste water is subjected to a series ofoperations to separate solids from the liquid phase of the waste waterand to biologically treat the waste water to break down organiccomponents. The separated solids are stored for further treatment orconversion into useful materials. The treated liquid phase can be put tovarious uses. In one embodiment, the treated liquid is recycled as flushwater for flushing animal waste from an animal barn, whereby little orno liquid phase escapes the system into the surrounding environment.

In one embodiment of the invention, a system for treating waste waterthat includes liquid components and solids components comprises askimmer apparatus comprising a holding tank and a solids receptacleadjacent thereto. The skimmer apparatus has an inlet for receiving thewaste water and a liquid outlet arranged below a level of an uppersurface of the waste water in the holding tank through which liquidoutlet the waste water is discharged from the holding tank. The skimmerapparatus further comprises a skimmer arranged for movement across theholding tank to skim floating solids from the upper surface of the wastewater, and a solids receptacle for receiving the solids skimmed by theskimmer. The system also includes a screening apparatus arranged toreceive the waste water from the liquid outlet of the skimmer apparatus,the screening apparatus being structured and arranged to screen thewaste water to remove coagulated suspended solids therefrom so as tocreate a solids stream and a liquid stream. Additionally, the systemcomprises a biological reactor arranged to receive the liquid streamfrom the screening apparatus, the biological reactor comprising a tankfor holding the waste water received from the screening apparatus, andan aerator disposed within the tank and operable to inject air into thewaste water therein for biologically treating the waste water, thebiological reactor having an outlet for discharging treated waste watertherefrom.

When the system is used in connection with an animal barn having a wasteremoval system for flushing animal waste produced by the animals fromthe animal barn, waste water treated in the biological reactor can befed to the inlet of the waste removal system of the animal barn to beused as flush water to flush animal waste therefrom, and the flush waterand animal waste from the animal barn can be fed into the inlet of theskimmer apparatus. Thus, the liquid phase of the effluent stream fromthe animal barn is continuously recycled through the barn and thetreatment system so that little or no liquid is released to thesurrounding environment.

The air injected into the waste water in the biological reactor ispreferably heated so as to maintain the waste water above a minimumtemperature necessary for the biological reaction to occur. Accordingly,the waste water is heated to an elevated temperature. If the heatedwaste water were fed back to the animal barn during warm conditions suchas during the summer, the temperature in the barn may become higher thandesired. In accordance with one embodiment of the invention, during warmambient conditions, the waste water can be fed from the biologicalreactor into a holding reservoir (e.g., a pond) where the water can becooled before being fed back to the barn. Conversely, during coldambient conditions, the holding reservoir can be bypassed such that theelevated-temperature water when fed to the animal barn helps heat thebarn.

The skimmer apparatus preferably comprises a variable-geometry gate at adischarge end of the holding tank adjacent the solids receptacle. Thevariable-geometry gate is movable between a closed position in which thegate prevents floating solids in the holding tank from passing into thesolids receptacle, and an open position in which the gate allows thefloating solids to be swept by the skimmer into the solids receptacle.In one advantageous embodiment, the variable-geometry gate comprises afixed lower portion and a movable upper portion. The upper portion inthe closed position of the gate engages the lower portion. In the openposition of the gate, the upper portion is pivoted away from the lowerportion to create an opening through which the floating solids are sweptby the skimmer into the solids receptacle. The movable upper portion canbe pivoted by mechanical action of the skimmer as it draws near thegate; for example, the skimmer can support one or more arms that pushthe upper portion open.

The skimmer apparatus advantageously also comprises a pump systemconnected to the liquid outlet of the holding tank, and a control systemoperable to control the operation of the pump system. The control systemis operable to cause the pump system to pump liquid out from the liquidoutlet so as to lower the level of the upper surface of the waste waterin the holding tank to a level allowing floating solids to be swept intothe solids receptacle. The control system also controls movement of theskimmer across the holding tank. Once the level of the waste water islowered, the skimmer is started across the tank to skim the floatingsolids from the surface and sweep them into the solids receptacle.

The skimmer apparatus in one embodiment includes a defoamer for knockingdown the thick layer of frothy foam that can form on the upper surfaceof the waste water in the holding tank of the apparatus and can cling tothe side walls and other surfaces. The defoamer preferably comprises awater spray system for spraying water on the foam. The water spraysystem can comprise a pipe closed at both ends and fed with waterthrough a T-junction or the like, and mounted on the traversing skimmerso that it extends transversely across the holding tank. The pipe canhave outlet holes spaced apart along its length for spraying water ontothe foam. As the skimmer moves across the tank, the water spray knocksdown the foam.

The system can also include an equalization tank arranged between theskimmer apparatus and the screening apparatus for holding the wastewater discharged from the skimmer apparatus for a period of time priorto treatment by the screening apparatus, the equalization tank servingto even out time-wise fluctuations in concentrations of waste componentsof the waste water fed to the screening apparatus and biologicalreactor. In this manner, the downstream components and system processesare not subjected to large “spikes” in waste concentration.

The system can also include a system for introducing a coagulant intothe waste water prior to the waste water being fed to the screeningapparatus so as to cause solids in the waste water to coagulate tofacilitate removal by the screening apparatus. The system forintroducing a coagulant advantageously comprises a serpentine flowpassage for increasing the residence time of a mixture of the wastewater and the coagulant. In one embodiment, the serpentine flow passageis defined by a plurality of elongate vertical tubes arranged one afteranother in a generally parallel array. The mixture of waste water andcoagulant is fed into the bottom end and out the top end of each tube insequence.

In one embodiment, a settling tank is arranged to receive the liquidstream from the screening apparatus and operable to allow suspendedsolids in the liquid stream to settle to a bottom of the settling tankas sludge, the settling tank having a sludge outlet for discharging thesludge and a liquid outlet for discharging liquid. Advantageously, thereis a connection between the sludge of the settling tank and the inlet ofthe skimmer apparatus for feeding the sludge back to the skimmerapparatus. In this manner, the sludge is sent back through the system toallow more solids to be skimmed, coagulated and separated, therebyreducing the load on the biological reactor.

The system can also include a clarifier arranged to receive treatedwaste from the biological reactor. The system can be arranged such thatsludge created in the clarifier is fed back into the skimmer apparatus.

The invention also provides a skimmer apparatus for separating wastewater into a first component comprising predominantly solids and asecond component comprising predominantly liquid. The skimmer apparatuscomprises a holding tank for holding a quantity of the waste water in asubstantially quiescent state such that solids in the waste water floatto the surface, a solids receptacle adjacent a discharge end of theholding tank, a skimmer movable across the holding tank for skimmingfloating solids from the surface of the waste water into the solidsreceptacle, and a variable-geometry gate at the discharge end of theholding tank adjacent the solids receptacle. The variable-geometry gateis movable between a closed position in which the gate prevents floatingsolids in the holding tank from passing into the solids receptacle, andan open position in which the gate allows the solids to be swept by theskimmer into the solids receptacle. The variable-geometry gate comprisesa fixed lower portion and a movable upper portion, the upper portion inthe closed position of the gate engaging the lower portion, the upperportion in the open position of the gate being pivoted away from thelower portion to create an opening in the gate through which thefloating solids are swept by the skimmer into the solids receptacle.

The skimmer apparatus advantageously also comprises a pump systemconnected to the liquid outlet of the holding tank, and a control systemoperable to control the pump system, the control system being operableto cause the pump system to pump liquid out from the holding tank so asto lower the level of the surface of the waste water in the holding tankto a level allowing the floating solids to be swept into the solidsreceptacle, and thereafter to cause the skimmer to begin moving acrossthe holding tank towards the discharge end thereof. Preferably, thecontrol system is operable to periodically cycle operation of the pumpsystem and skimmer so that discharging of liquid from the holding tankand skimming of solids into the solids receptacle occur on a periodicbasis.

The invention also provides a screening apparatus for treating a mixturecontaining liquid and solids. The solids can comprise animal waste aswell as hair. The screening apparatus comprises a fine-mesh screenarranged in an inclined orientation, the screen having an upper end anda lower end and having an upper surface, the screen allowing liquid toflow downwardly through apertures therein while preventing solids largerthan the apertures from passing through the screen. The apparatus alsoincludes an inlet arranged proximate the upper end of the screen forfeeding the mixture onto the upper surface of the screen such that themixture flows downward along the screen toward the lower end thereof. Aplurality of substantially liquid-impervious squeegees are connected toa drive member arranged in an endless loop and driven by a motor, thesqueegees being spaced apart about the loop of the drive member, thesqueegees contacting the upper surface of the screen and being driven bythe drive member to move downward along the upper surface of the screenso as to scrape solids from the screen. The squeegees also serve as damsoperable to prevent the mixture from flowing past the squeegees alongthe screen such that residence time of the mixture on the screen isincreased.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a diagrammatic depiction of a system and process for treatingwaste flushed from an animal barn in accordance with one embodiment ofthe invention;

FIG. 2A is a schematic representation of a skimming apparatus inaccordance with one embodiment of the invention, wherein thevariable-geometry gate is closed and the waste water level is relativelyhigh;

FIG. 2B is a view similar to FIG. 2A, showing the waste water levelhaving been lowered and showing the skimmer having been moved across thetank to sweep floating solids into the solids receptacle;

FIG. 3 is a side view of a screening apparatus in accordance with theinvention; and

FIG. 4 is a view of the screening apparatus along the directionindicated by line 4-4 in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

The present inventions now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the invention are shown. Indeed, these inventions may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

A waste water treatment system in accordance with one embodiment of thepresent invention is depicted in FIG. 1, for treating waste watergenerated in an animal husbandry operation, such as hog farming. Ananimal barn or hog house 10 houses animals. In one particular type ofanimal barn, the floor of the barn is slotted so that animal waste fallsdown through the floor into a subfloor space below the slotted floor. Aflush system or waste removal system (not shown) can be used toperiodically flush the subfloor space with water to flush the animalwaste out from the animal barn; the flushed animal waste and flushwater, which collectively are referred to herein as waste water, exitthe animal barn from an outlet 12.

In accordance with one embodiment of the invention as depicted in FIG.1, the waste water is treated in a treatment system and process, and isthen recycled back to the animal barn 10 as flush water. Accordingly,little or no liquid waste escapes from the system into the surroundingenvironment. The primary components of the treatment system include askimmer apparatus 20, a coagulation system 30, a screening apparatus 40,a biological reactor 50, and a clarifier 60. Additional components aredescribed below.

The waste water from the animal barn 10 is fed into the skimmerapparatus 20. Prior to feeding the water into the skimmer apparatus, thewater optionally can be passed through a separation box 14 that includesa grate or the like for separating and removing large objects (e.g.,trash that falls through the animal barn floor into the subfloor space,bones of animals that die in captivity and are cannibalized by the otheranimals, etc.). Where the skimmer apparatus is at a higher verticallevel than the barn, the waste water can be fed into an optional pumpingor lift station 16 operable to raise the waste water up to a suitablelevel. The water is then fed into the skimmer apparatus.

The skimmer apparatus 20, which is described in further detail below inconnection with FIGS. 2A and 2B, provides an initial, physicalseparation of the waste water into two phases, namely, a predominantlyliquid phase and a high-solids-content phase (also referred to herein assludge). The skimmer apparatus accomplishes this initial separation byallowing the waste water to sit in a quiescent state in a holding tankor skimmer pit 22 for a period of time to allow some of the solids tofloat to the surface, and skimming the floating solids off the surfaceinto a solids receptacle 24 adjacent the skimmer pit. Solids from thesolids receptacle are fed into a sludge tank 25 where they are held fora period of time. The sludge tank can be emptied periodically and thesolids or sludge can be put to various uses or further treated in otherprocesses that are not described herein.

The predominantly liquid phase from the skimmer apparatus 20 is fed intoan equalization tank 26, which holds a large quantity of the liquid.Although some of the solids are removed in the skimmer apparatus, thewaste water still contains some amount of solids. The equalization tank26 functions to reduce the variability in the solids concentration ofthe waste water that is passed to the next downstream process in thesystem, and thereby prevents large “spikes” in solids concentration frompassing through the system.

From the equalization tank 26, the waste water preferably is fed to thecoagulation system 30 before being screened in the screening apparatus40. The coagulation system operates to coagulate some of the remainingsolids in the waste water, some of which are in the form of finesuspended masses, so that the fine masses tend to agglomerate intolarger masses that can be removed by the screening apparatus. To thisend, the coagulation system includes a coagulant feed 32 operable tofeed a coagulant (typically a polymer material) into the waste water.The coagulation system may also include a static mixer 34 or other typeof mixing device for mixing the coagulant into the waste water toimprove the uniformity of dispersion of the coagulant. The waste waterpreferably is then passed through an array 36 of elongate vertical (orgenerally vertical) tubes in serpentine fashion. The array 36 isdesigned to increase the residence time of the waste water and coagulantmixture before it reaches the screening apparatus. The tubes arearranged generally parallel to each other. The waste water is fed intothe bottom end of one tube and emerges from the top end of the tube,then is led back down and fed into the bottom end of the next tube andout the top end of the tube, and so on in serpentine fashion. As analternative to the use of a plurality of separate tubes, other types ofarrangements for creating a long flow passage could be used, such as asingle tube formed into a serpentine shape, or other structure.

The waste water is fed from the coagulation system 30 to the screenseparator or screening apparatus 40, where the coagulated solids andother solid materials are screened out from the water. The solidsseparated out by the screening apparatus are ultimately transferred intothe sludge tank 25, while the liquid is passed on to the next step ofthe treatment process. The screening apparatus is further describedbelow in connection with FIGS. 3 and 4.

The waste water discharged from the screening apparatus 40 is fed into afeed tank 42 (not illustrated in detail in the drawings), which holds arelatively large quantity of the waste water. The feed tank's inlet islocated in one side wall of the tank, and a liquid outlet is arranged inthe same or a different side wall, preferably at a higher vertical levelthan the inlet. The feed tank can also include a skimmer for skimmer anyfloating solids from the surface of the water into a collection troughor the like. Some settling of solids occurs in the feed tank;accordingly, there is a sludge outlet at the bottom of the tank. Thesludge formed at the bottom of the feed tank (and any skimmed solids) isfed into a sludge thickener 44, which constitutes a large tank where thesludge is held until it can be pumped out to the solids receptacle 24 ofthe skimmer apparatus, from which it ultimately is fed into the sludgetank 25.

The predominantly liquid waste water in the feed tank 42 is dischargedfrom the liquid outlet of the feed tank and fed into the biologicalreactor 50. Depending on the needed capacity of the system, there couldbe more than one such reactor. The biological reactor comprises a tankfor holding the waste water, and an aeration system (not shown) forinjecting air into the waste water so as to oxygenate the water andpromote biological breakdown of organic substances in the water. Themicroorganisms that effect the breakdown tend to become inactive if thetemperature of the water falls below about 65° F. Accordingly, the airinjected into the water preferably is heated to a level sufficient toensure that the water in the reactor remains above 650 F, and morepreferably remains at about 80° F. to 85° F. To accomplish this, the airpreferably is heated to about 900 F to 100° F. above the ambienttemperature.

The aeration system preferably is operable to create very fine airbubbles in the waste water. Various types of aerating devices can beused in the practice of the invention. One suitable type comprises anelastomeric membrane having a plurality of small slits that open up tocreate small openings when the membrane is inflated by pressurized air,but that substantially close up when the membrane is not inflated. Themembrane can comprise a sleeve that fits closely about a circular pipe(e.g., a PVC pipe) that is supplied with pressurized air through itscentral passage and that has a plurality of radial holes extending fromthe central passage to the outer surface of the pipe, for example asshown in U.S. Pat. No. 5,234,632. Alternatively, the membrane can be inthe form of a disc forming one wall of a pressurized chamber. Othertypes of aerating devices can also be used. A plurality of such devicestypically are distributed at the bottom of the biological reactor.

The treated waste water from the biological reactor 50 is fed to aclarifier 60. The clarifier is generally similar in design and operationto the feed tank 42 previously described, although the liquid outlet ofthe clarifier preferably is located near the top end of the tank. Theclarifier holds the treated waste water for a sufficient period of timefor the suspended biological sludge to settle into the bottom of thetank by gravity and to separate from the treated wastewater. Sludgeformed in the clarifier is fed to the sludge thickener 44. The clarifiercan be a simple tank that allows gravity separation. However, it shouldbe recognized that chemical flocculating agents may be used if necessaryto cause a suspended sludge to settle. Various clarifiers have beendeveloped that could be suitably used in the practice of the invention,although it is typically not necessary to use clarifiers of more complexdesign.

The clarified liquid phase of the waste water is fed from the clarifierto the clear well 70. The clear well 70 is typically an open, stirredtank that can be kept within the same building as the clarifier. Theclear well serves to hold water from the waste water treatment system ata constant temperature for recirculation to the animal barn for use asflush water. The flush water helps to dilute and liquefy the animalwaste for ease in transferring the collected animal waste to separationbox 14 in accordance with the invention. The clear well is able tomaintain the clarified waste water at a suitable temperature duringwinter conditions because it is typically maintained indoors, or can beseparately heated, if necessary, for use as a recharge to the animalbarn in the winter.

As noted, heated air is bubbled through the waste water in thebiological reactor, and hence the water in the clear well 70 is at anelevated temperature relative to the temperature it otherwise wouldhave. During warm ambient conditions (e.g., during summer), recyclingthe elevated-temperature water back to the animal barn 10 might tend toraise the temperature in the barn to an undesirable level. Accordingly,during such warm conditions, the water can be fed from the clear well toa holding reservoir or pond 80 where the water can be retained for aperiod of time so that it cools before being recycled to the barn. Someof the water in the holding reservoir can be sprayed on nearby fields 90if desired. Conversely, during cold ambient conditions (e.g., duringwinter), the barn may need to be heated to maintain the temperatureinside the barn at the desired level. The elevated-temperature water inthe clear well can assist in the heating, and hence during such coldconditions, the holding reservoir can be bypassed and the water can befed directly from the clear well to the barn.

The skimmer apparatus 20 is now described in greater detail withreference to FIGS. 2A and 2B. As previously noted, the skimmer apparatuscomprises a skimmer pit or holding tank 22 within which a solidsreceptacle 24 is disposed. The holding tank 22 is formed by a bottomwall 92 (which preferably is slightly inclined in the direction towardthe solids receptacle, as shown) and a plurality of side walls 94upstanding from the bottom wall. Waste water is received into theholding tank through an inlet 95, which preferably is arranged to dumpthe waste water into the solids receptacle. The holding tank has aliquid outlet 96 located in one of the side walls some distance abovethe bottom wall for discharging predominantly liquid waste water. Anoutlet conduit 98 is connected to the liquid outlet. A pump 100 and acontrollable valve 102 are arranged in the outlet conduit; a controlsystem 104 is connected to the pump and valve for controlling theiroperation, as further described below.

The waste water received in the holding tank 22 is allowed to remain inthe tank in a quiescent state for a certain period of time so that someof the solids in the waste water can float to the surface as shown inFIG. 2A. The solids receptacle 24 essentially comprises a sieve-likestructure, preferably formed as a V-shaped trough 106 located a distanceabove the bottom wall 92 of the tank 22 and extending transverselyacross the tank from one side wall substantially to an opposite sidewall. The walls of the trough 106 are perforated to allow liquid tofreely pass through the walls while preventing larger bodies of solidsfrom passing through. Located adjacent the trough 106 is a gate having amovable portion 108 that is pivotally mounted at its upper edge tosuitable fixed structure in the skimmer apparatus. The movable portion108 is pivotable about its upper edge between a closed position (FIG.2A) in which the lower edge of the movable portion engages one wall ofthe trough 106 (which constitutes a fixed portion of the overall gatestructure) so as to form a wall essentially separating the solidsreceptacle from the rest of the tank, and an open position (FIG. 2B) inwhich the movable portion 108 is pivoted away from the trough 106 so asto form an opening 110 through which floating solids in the holding tankcan be moved into the solids receptacle 24. The movable portion 108 canbe moved by various mechanisms, including but not limited to a suitableactuator (not shown) such as a pneumatic or hydraulic cylinder orelectric motor, which actuator can also be controlled by the controlsystem 104. However, as further described below, in the preferredembodiment, the movable portion 108 is simply pushed open by the skimmerof the skimmer apparatus when it nears the trough 106.

One or more water level sensors 119 are arranged in the holding tank forsensing the level of the upper surface of the water. The sensor 119 cancomprise a float-type device or other suitable sensor capable ofdetecting the water level in the tank. The sensor 119 is connected tothe control system 104 that controls the operation of the pump and valvein the outlet conduit 98. Although not illustrated, it will beunderstood that similar pump and valve equipment is included in theinlet conduit system that feeds the waste water into the holding tank,and such pump and valve equipment is also controlled by the controlsystem 104. The control system is able to control the water level in theholding tank by suitably controlling the various pumps and valves.During the quiescent holding period when solids are allowed to float tothe surface, the water level is controlled to be well above the top ofthe trough 106, as shown in FIG. 2A.

When it is desired to skim off the floating solids, the valve 102 isopened and the pump 100 is operated to pump liquid out from the holdingtank 22 to the equalization tank 26 (FIG. 1) until the upper surface ofthe water in the holding tank is at a predetermined level (e.g., about12 inches above the top end of the trough 106). The skimmer apparatusincludes a skimmer 114 mounted on a suitable traversing mechanism suchas the schematically illustrated chain and sprocket system 116 so thatthe skimmer can be traversed across the holding tank. The skimmercomprises a plate or the like fixed to the traversing mechanism at itsupper end and extending downward toward the bottom wall of the holdingtank. The lower end of the skimmer is slightly lower than the upper edgeof the trough 106. The traversing mechanism is operated to cause theskimmer 114 to slowly move across the holding tank from the end farthestfrom the solids receptacle toward the end nearest the solids receptacle.The skimmer can include one or more arms 112 that project from theskimmer in the direction of the solids receptacle and that push open themovable gate portion 108 as the skimmer nears the solids receptacle. Theskimmer pushes the floating solids through the resulting opening 110into the solids receptacle as shown in FIG. 2B.

Next, the pump system is operated to lower the water level in theskimmer apparatus still further, so that the water level is below thebottom of the trough 106. As noted, the walls of the trough 106 areperforated with holes sized to allow the liquid to pass through whilesubstantially preventing the solids from passing through. Consequently,a substantial proportion of the solids remain in the trough 106.

Preferably, an auger 113 is arranged at the bottom of the trough forconveying the solids in the trough to one end thereof, where the solidsare dumped into a receiving area, which is arranged below the trough inthe illustrated embodiment. A suitable conveyor, such as a screwconveyor or auger 120, periodically conveys solids out of the solidsreceiving area into the sludge tank 25 (FIG. 1).

The skimmer is then traversed back to its starting position at theopposite end of the holding tank. The pump system is operated to pumpmore waste water into the holding tank to begin another cycle ofoperation. This cyclic operation is repeated on a regular periodicbasis, such as once every 24 hours, or any other suitable period oftime.

The skimmer apparatus can include a defoamer for knocking down thethick, frothy layer of foam that can tend to form at the surface of thewaste water in the tank. The defoamer in one embodiment comprises a pipe115 mounted on the traversing skimmer 114 and fed with water by anattached hose as shown. The pipe 115 extends across the width of thetank 22. The pipe is capped at one end (if the hose feeds into theopposite end) or at both ends (if the hose is connected to the pipethrough a T-junction), and has holes in its side wall spaced apart(e.g., every 12 inches) along the length of the pipe. Thus, water pumpedto the pipe sprays out from the holes for knocking down the foam. Thewater can be pumped from the tank 22 so that the defoamer systemessentially forms a recirculating system.

The skimmer apparatus 20 also includes a sludge outlet 118 in the bottomwall of the holding tank. Some solids in the waste water tend to settleat the bottom and collect to form a sludge. During each cycle ofoperation of the skimmer apparatus, sludge is pumped out from the sludgeoutlet 118 and fed to the sludge thickener 44 (FIG. 1). As previouslynoted, the sludge from the sludge thickener is then recycled back to thesolids receptacle.

The screening apparatus 40 is now described in further detail withreference to FIGS. 3 and 4. The screening apparatus includes a metalscreen 122 that is inclined relative to horizontal. The screen hasopenings suitably sized so that the coagulated solids formed in thecoagulation system 30 (FIG. 1) and other solids in the waste water(e.g., animal hair) tend not to be able to pass through the openings,while liquid phase can pass through. Formed beneath the screen is aliquid collector or pan 124 for catching liquid that passes through thescreen from its upper surface through the openings and out from thelower surface of the screen. A liquid outlet 126 is connected to the pan124 for conducting the liquid to the feed tank 42 (FIG. 1). Arrangedbelow the lower edge of the screen is a solids collector 128 forcatching solids that are swept off the upper surface of the screen by asweeping system 130.

The sweeping system 130 comprises a plurality of spaced squeegees 132made of rubber or the like, driven to move along the upper surface ofthe screen 122 from the upper edge toward the lower edge thereof. Thesqueegees are substantially impervious to liquid. The sweeping systemincludes a pair of endless chain loops 134 adjacent opposite sides ofthe screen, each chain being looped about a pair of sprockets 136respectively located near the upper and lower ends of the screen. Thesprockets near the lower end of the screen are mounted on a common shaft138 that extends transversely above the screen, and the sprockets nearthe upper end of the screen are mounted on a common shaft 138 thatextends transversely above the screen. One of the shafts 138 constitutesa drive shaft rotatably driven by a suitable motor (not shown) forrotating the chain loops. The squeegees 132 are affixed to the chainloops, and the chains drive the squeegees so they are scraped along theupper surface of the screen.

The screening apparatus also includes a waste water feed box or nozzle140 located adjacent the upper end of the screen. The feed nozzle 140 isconfigured to extend across substantially the full width of the screenand to dump waste water onto the upper surface of the screen at itsupper end. Waste water from the polymer contact tubes 36 (FIG. 1) of thecoagulation system is fed into the feed nozzle via an inlet conduit 142connected to the nozzle. The waste water spills out from the nozzle ontothe screen.

As the squeegees 132 are swept down the upper surface of the screen,they act as dams that prevent the waste water from flowing down pastthem, thereby allowing liquid to pass through the screen into thecollector pan 124. Solids that cannot pass through the screen openingsare retained on the upper surface of the screen and are swept by thesqueegees into the solids collector 128.

When the screening apparatus is used in a hog farming waste watertreatment system as shown in FIG. 1, the openings in the screen must beappropriately sized to substantially prevent coagulated solids and othermaterials such as animal hair from passing through the screen. Theoptimum size of the openings depends on various factors including thecharacteristics of the solids in the waste water.

The system and method for treating waste water as described above can beused for treating waste water of various origins, including but notlimited to waste water generated in an animal husbandry operation suchas high-density hog farming, waste water generated in municipal sewagesystems, and waste water generated in industrial processes.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

1-20. (canceled)
 21. A system for treating a stream of animal wasteflushed from an animal barn with flush water, the stream having liquidcomponents and solid components, the system comprising: a skimmerapparatus comprising a holding tank for receiving the waste water andhaving a liquid outlet arranged below a level of an upper surface of thewaste water in the holding tank through which liquid outlet the wastewater is discharged from the holding tank, the skimmer apparatus furthercomprising a skimmer arranged for movement across the holding tank toskim floating solids from the upper surface of the waste water, and asolids receptacle for receiving the solids skimmed by the skimmer; asystem for introducing a coagulant into the waste water discharged fromthe liquid outlet of the holding tank so as to cause suspended solids inthe waste water to coagulate; a screening apparatus arranged to receivethe waste water having the coagulant therein, the screening apparatusbeing structured and arranged to screen the waste water to removecoagulated suspended solids therefrom so as to create a solids streamand a liquid stream; a settling tank arranged to receive the liquidstream from the screening apparatus and operable to allow suspendedsolids in the liquid stream to settle to a bottom of the settling tank,the settling tank having a solids outlet for discharging the settledsolids and a liquid outlet for discharging liquid, and a connectionbetween the solids outlet of the settling tank and the inlet of theskimmer apparatus for feeding the settled solids back to the skimmerapparatus; and a biological reactor arranged to receive the liquid fromthe settling tank, the biological reactor comprising a vessel forholding the liquid from the settling tank, and an aerator disposedwithin the vessel and operable to inject air into the liquid forbiologically treating the liquid, the biological reactor having anoutlet for discharging treated waste water therefrom.
 22. The system ofclaim 21, further comprising an animal barn for housing animals, theanimal barn having a waste removal system for flushing animal wasteproduced by the animals from the animal barn, the waste removal systemhaving an inlet for flush water used for flushing the animal waste fromthe animal barn and an outlet through which the flush water and animalwaste are discharged from the animal barn, and wherein the system isarranged such that waste water treated in the biological reactor is fedto the inlet of the waste removal system for the animal barn to be usedas flush water to flush animal waste therefrom, and the flush water andanimal waste from the animal barn are fed into the inlet of the skimmerapparatus.
 23. The system of claim 22, further comprising a clarifierarranged between the biological reactor and the animal barn for furthertreating the waste water before feeding the waste water back as flushwater for the animal barn.
 24. The system of claim 23, wherein the airinjected into the biological reactor is heated to a temperatureexceeding ambient temperature prior to injection into the waste water,such that the waste water in the biological reactor becomes elevated intemperature.
 25. The system of claim 24, further comprising a holdingreservoir, and wherein during cold ambient conditions theelevated-temperature waste water is fed from the clarifier back to theanimal barn bypassing the holding reservoir such that the waste waterhelps heat the animal barn, and during warm ambient conditions theelevated-temperature waste water is fed from the clarifier to theholding reservoir where the waste water is cooled prior to being fedback to the animal barn.
 26. The system of claim 25, further comprisinga clear well arranged to receive the elevated-temperature waste waterfrom the clarifier during both cold and warm ambient conditions, and thewaste water being fed from the clear well to the animal barn bypassingthe holding reservoir during cold ambient conditions, and being fed fromthe clear well first to the holding reservoir and then to the animalbarn during warm ambient conditions.
 27. A method for treating wastewater, the waste water having liquid components and solid components,the method comprising the steps of: holding a quantity of the wastewater in a quiescent state in a holding tank to allow solids to float tothe top of the waste water; skimming solids from the top of the wastewater and discharging liquid from the holding tank; treating the liquiddischarged from the holding tank with a coagulant to cause suspendedsolids in the liquid to coagulate; screening the liquid treated withcoagulant to removed coagulated solids therefrom; and aerating thescreened liquid in a biological reactor for biologically treating thewaste water.
 28. The method of claim 27, wherein heated air is injectedinto the liquid in the biological reactor so as to maintain the liquidabove a predetermined minimum temperature necessary for biologicalreaction to occur.
 29. The method of claim 28, wherein the waste watercomprises animal waste flushed from an animal barn with flush water, andfurther comprising the step of using liquid discharged from thebiological reactor as flush water for flushing animal waste from theanimal barn.
 30. The method of claim 29, wherein during cold ambientconditions the liquid from the biological reactor is fed back to theanimal barn along a first path, and during warm ambient conditions theliquid from the biological reactor is fed back to the animal barn alonga second path different from the first path, the second path including aholding reservoir for holding the liquid to allow the liquid to coolprior to being fed to the animal barn.
 31. The method of claim 29,further comprising the step of feeding the flush water and animal wastefrom the animal barn to the holding tank.
 32. The method of claim 27,further comprising the step of reducing time-wise fluctuations in solidsconcentration of the waste water by passing the waste water dischargedfrom the holding tank through an equalization tank.
 33. A skimmerapparatus for separating waste water into a first component comprisingpredominantly solids and a second component comprising predominantlyliquid, the skimmer apparatus comprising: a holding tank for holding aquantity of the waste water in a substantially quiescent state such thatsolids in the waste water float to the surface, the holding tank havinga liquid outlet; a solids receptacle adjacent one end of the holdingtank; a skimmer movable across the holding tank for skimming floatingsolids from the surface of the waste water into the solids receptacle; avariable-geometry gate at the discharge end of the holding tank adjacentthe solids receptacle, the variable-geometry gate being movable betweena closed position in which the gate prevents floating solids in theholding tank from passing into the solids receptacle, and an openposition in which the gate allows the floating solids to be swept by theskimmer into the solids receptacle, wherein the variable-geometry gatecomprises a fixed lower portion and a movable upper portion, the upperportion in the closed position of the gate engaging the lower portion,the upper portion in the open position of the gate being pivoted awayfrom the lower portion to create an opening in the gate through whichthe floating solids are swept by the skimmer into the solids receptacle.34. The skimmer apparatus of claim 33, further comprising: a pump systemconnected to the liquid outlet of the holding tank; and a control systemoperable to control the the pump system, the control system beingoperable to cause the pump system to pump liquid out from the holdingtank so as to lower the level of the surface of the waste water in theholding tank to a level allowing the floating solids to be swept intothe solids receptacle, and thereafter to cause the skimmer to beginmoving across the holding tank towards the discharge end thereof. 35.The skimmer apparatus of claim 34, wherein the control system isoperable to periodically cycle operation of the pump system and skimmerso that discharging of liquid from the holding tank and skimming ofsolids into the solids receptacle occur on a periodic basis.
 36. Theskimmer apparatus of claim 33, wherein the holding tank has a sludgeoutlet arranged at a bottom of the holding tank for discharging sludgethat has settled to the bottom.
 37. The skimmer apparatus of claim 33,further comprising a conveyor arranged to convey solids out from thesolids receptacle.
 38. The skimmer apparatus of claim 37, wherein theconveyor comprises a screw conveyor.
 39. The skimmer apparatus of claim33, wherein the solids receptacle is disposed within the holding tankadjacent the one end thereof, the solids receptacle being formed byperforated walls that allow liquid to freely pass therethrough whilepreventing at least some solids from passing.
 40. The skimmer apparatusof claim 39, wherein one of the walls of the solids receptacle forms thefixed lower portion of the gate.
 41. The skimmer apparatus of claim 39,wherein an inlet for feeding waste water into the skimmer apparatus isarranged such that the waste water is fed into the solids receptacle sothat larger bodies of solids are screened out by the solids receptacle.42. The skimmer apparatus of claim 33, wherein the skimmer is structuredand arranged to push the movable upper portion of the gate open when theskimmer nears the gate.
 43. The skimmer apparatus of claim 33, furthercomprising a defoamer operable to spray water onto the surface of thewaste water in the holding tank to knock down foam that forms on thesurface.
 44. The skimmer apparatus of claim 43, wherein the defoamer ismounted on the skimmer.
 45. A screening apparatus for treating a mixturecontaining liquid and solid animal waste, comprising: a fine-mesh screenarranged in an inclined orientation, the screen having an upper end anda lower end and having an upper surface, the screen allowing liquid toflow downwardly through apertures therein while preventing solids largerthan said apertures from passing through the screen; an inlet arrangedproximate the upper end of the screen for feeding the mixture onto theupper surface of the screen such that the mixture flows downward alongthe screen toward the lower end thereof; and a plurality ofsubstantially liquid-impervious squeegees connected to a drive memberarranged in an endless loop and driven by a motor, the squeegees beingspaced apart about the loop of the drive member, the squeegeescontacting the upper surface of the screen and being driven by the drivemember to move downward along the upper surface of the screen so as toscrape solids from the screen, the squeegees also serving as damsoperable to prevent the mixture from flowing past the squeegees alongthe screen such that residence time of the mixture on the screen isincreased.